GaN type semiconductor device

ABSTRACT

A GaN type semiconductor layer having a new structure is provided which incorporates a substrate having surface which is opposite to a GaN type semiconductor layer and which is made of Ti.

This application is a divisional Application of U.S. patent applicationSer. No. 09/525,425 filed Mar. 14, 2000, now U.S. Pat. No. 6,335,217application Ser. No. 09/170,128 filed Oct. 13, 1998, now U.S. Pat. No.6,100,545.

BACKGROUND OF THE INVENTION

The present invention relates to a GaN semiconductor and/or its relatedmaterial's device (AlGaInN semiconductor device).

A fact has been known that the GaN type semiconductor device can beemployed as, for example, a blue light emitting device. A light emittingdevice of the foregoing type incorporates a substrate usually made ofsapphire.

The sapphire substrate has the following problems which must be solved.That is, since the sapphire substrate is transparent, light emitted fromthe light emitting device and required to be extracted from the uppersurface of the device undesirably penetrates the sapphire substratewhich is formed in the opposite surface of the device. Therefore, lightemitted by the light emitting device cannot effectively be used.

Moreover, the sapphire substrate is still an expensive substrate.

In addition, since the sapphire substrate is an insulating material, theelectrodes must be formed on same side of the substrate. Thus, a portionof the semiconductor layer must be etched. It leads to a fact that thebonding process is doubled. Since both of n and p electrodes are formedon one side, reduction in the size of the device has been limited. Whatis worse, a problem of charge up arises.

Although use of a Si (silicon) substrate in place of the sapphiresubstrate may be considered, growth of a high quality AlGaInNsemiconductor layer on the Si substrate is very difficult. One of causesis the difference in the coefficient of thermal expansion between Si andthe GaN type semiconductor. In contrast with the linear coefficient ofthermal expansion of Si which is 4.7×10⁻⁶/K, the linear coefficient ofthermal expansion of CaN is 5.59×10⁻⁶/K which is larger than the formervalue. Therefore, if the GaN semiconductor layer on Si is cooled afterit is grown, the Si substrate is expanded. Thus, the device is deformedsuch that the semiconductor layer portion of the GaN is compressed.There is apprehension that tensile stress is generated and thus a crackis formed. Even if no crack is formed, lattices are distorted.Therefore, a required function of the AlGaInN type semiconductor devicecannot be exhibited.

SUMMARY OF THE INVENTION

In view of the foregoing, an object of the present invention is toprovide a new AlGaInN semiconductor device.

Another object of the present invention is to provide a laminatedmaterial which serves as an intermediate material of an AlGaInNsemiconductor device and which has a new structure.

Accordingly, inventors of the present invention have made energeticstudies to found a new substrate on which an AlGaInN semiconductor layercan satisfactorily be grown. As a result, the following facts are found.

That is, to heteroepitaxially grow an AlGaInN semiconductor on asubstrate, at least two factors of the five factors below must besatisfied:

(1) Excellent adhesiveness between the AlGaInN type semiconductor andthe substrate is required.

(2) The coefficients of thermal expansion of the AlGaInN semiconductorand the substrate must be close to each other.

(3) The substrate must have a low elastic modulus.

(4) The crystalline structure of the substrate must be the same as thatof the AlGaInN semiconductor.

(5) |lattice constant of the substrate−lattice constant of the AlGaInNsemiconductor|/lattice constant of the AlGaInN semiconductor≦0.05 mustbe satisfied (that is, the difference between the lattice constant ofthe substrate and the lattice constant of the AlGaInN semiconductorlayer must be ±5% or lower).

As a matter of course, it is preferable that at least three factors ofthe five factors are satisfied, more preferably at least four factorsare satisfied and most preferably all of the five factors are satisfied.

As a material which is capable of satisfying the above-mentionedfactors, some metal materials are paid attention. Among the metalmaterials, Ti is paid attention especially.

The substrate must have a structure that at least its surface, that is,a surface which is in contact with the AlGaInN semiconductor layer mustsatisfy the foregoing factors.

Therefore, the base material of the substrate may be made of anappropriate material and the surface portion of the substrate may bemade of a material which is able to satisfy the above-mentioned factors.

Similarly to the sapphire substrate, a buffer layer made ofAl_(a)In_(b)Ca_(1-a-b)N including a=0, b=0 or a=b=0) such as AlN or GaN,may be interposed between the semiconductor layer and the substrate.

On the other hand, a semiconductor device can be constituted which has astructure that a buffer layer for buffering stress is interposed betweenthe Si substrate and the AlGaInN semiconductor layer. As a material forconstituting the buffer layer for buffering stress, some metal materialsare paid attention. Among the materials, Ti is paid attentionespecially. That is, a semiconductor device has a structure that a Tilayer is formed on a Si substrate and a CaN type semiconductor layer isformed on the Ti layer.

The present invention has been found on the basis of the aforementionedmatters. That is, according to a first aspect of the present invention,there is provided an AlGaInN type semiconductor device comprising:

an AlGaInN type semiconductor layer;

a substrate having a surface which is contact to the semiconductor layerand which is made of Ti.

If the thus structured semiconductor device has a structure that theAlGaInN type semiconductor layer has a structure of the light emittingdevice, the substrate serves as a reflecting layer. Therefore, lightemitted by the device can effectively be used.

Thus an individual reflecting layer which has been required for a lightemitting device or a light receiving device such as sensor or solar cellincorporating a transparent sapphire substrate is not required.Moreover, a necessity of removing a process for removing a substrate canbe eliminated in a case where the substrate is made of a material, suchas GaAs, which absorbs light.

The AlGaInN semiconductor is a nitride semiconductor in a group IIIgenerally expressed by Al_(x)Ga_(y)In_(1-x-y)N (0≦x≦1, 0≦y≦1, 0≦x+y≦1).An appropriate dopant may be contained.

Each of the light emitting devices has a known structure in which alight emitting layer is interposed between the different conductivesemiconductor layers (clad layers). The light emitting layer used is asuperlattice structure or a double hetero structure.

An electronic device such as an FET (Field Effect Transistor) may beformed by an AlGaInN semiconductor.

The AlGaInN semiconductor layer is formed by a known metal organicchemical vapor deposition method (hereinafter called a “MOCVD”). Also aknown molecular beam epitaxy (an MBE method) may be employed.

The substrate must have a structure that its surface, that is, thesurface which is to contact the AlGaInN type semiconductor layer, ismade of Ti. Therefore, at least the surface layer of the substrate maybe made of Ti and the lower layer (the base layer) may be made of anappropriate material. Another structure may be employed in which thebase layer is made of a Ti material or a Ti alloy. Moreover, the surfacelayer is formed by Ti having a high quality.

It is preferable that the surface contact to the AlGaInN semiconductorlayer is made of single crystal Ti. Under condition that the crystallinestructure is substantially maintained, Ti may be replaced by the Tialloy. Maintaining the crystalline structure means that the Ti alloy hasthe c plane such as (1 1 1) or (0 0 0) like Ti.

It is preferable that the overall body of the substrate has an electricconductivity. If the substrate has the electric conductivity, currentcan be supplied to the AlGaInN type semiconductor layer through thesubstrate by connecting an electrode to the substrate. Therefore,complicated etching of the semiconductor layer which has been requiredto constitute the light emitting device or the light receiving device bythe AlGaInN type semiconductor layer can be eliminated. In an exampleshown in FIG. 21, the n clad layer can electrically be connected to theoutside through the substrate. In a case of the sapphire conventionalsubstrate which is an insulating substrate, the light emitting layer andthe p clad layer must be etched so as to be exposed and electricallyconnected to the outside.

Since supply of current from the substrate to the semiconductor layer ispermitted, bonding to an external power source can easily be performed.

If an electrical earth is established, the problem of charge up caneasily be overcome.

To make the substrate to be electrically conductive, the base layer ofthe substrate is made of an electrically conductive metal material, suchas Cr, Hf, Nb, Re, Ta, Ti, V, Zr or Y or Si, GaAs, GaP, InP, ZnO orZnSe.

The thus-formed base layer is subjected to CVD (Chemical VapourDeposition), such as plane CVD, thermal CVD or light CVD, or sputteringor evaporation (Physical Vapour Deposition) so that a Ti layer isformed.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a graph showing dependency of the crystallinity of a Ti layerevaporated on a sapphire base layer on the thickness;

FIG. 2 is a chart showing results of φ (PHI) scan of the Ti layerevaporated on the sapphire base layer;

FIG. 3 is a graph shoving dependency of the crystallinity of the Tilayer evaporated on the sapphire base layer on the evaporation speed;

FIG. 4 is a graph showing dependency of the crystallinity of the Tilayer evaporated on the sapphire base layer on an evaporationtemperature;

FIG. 5 is a graph showing the relationship between the crystallinity ofthe Ti layer and a heat treatment temperature when the Ti layerevaporated on the sapphire base layer has been subjected to heattreatment;

FIG. 6 is a chart showing results of 2θ-ω scan for evaluating thecrystallinity of a GaN layer grown on an AlN buffer layer formed on theTi layer formed on the sapphire base layer;

FIG. 7 is a chart showing results of φ (PHI) scan of the same sample asthat shown in FIG. 6;

FIG. 8 is a chart showing results of 2θ-ω scan for evaluating thecrystallinity of a CaN layer grown on an AlGaN buffer layer formed onthe Ti layer formed on the sapphire base layer;

FIG. 9 is a chart showing results of φ (PHI) scan of the same sample asthat shown in FIG. 8;

FIG. 10 is a chart showing a rocking curve for evaluating thecrystallinity of GaN grown on the Ti/sapphire through an AlGaN bufferlayer;

FIG. 11 is a graph showing the relationship between a growth temperatureof the AlGaN buffer layer and the crystallinity of GaN;

FIG. 12 is a graph showing the relationship between a gas flow ratio ofTMG end TMA carrier gases for forming the AlGaN buffer layer and thecrystallinity of GaN;

FIG. 13 is a graph showing the relationship between a temperature forthermal treatment of the Ti/sapphire and the crystallinity of GaN.

FIG. 14 is a chart showing results of φ (PHI) scan of the (1 0 1 -2)plane of the Ti layer evaporated on the (111) plane of the Si substrate;

FIG. 15 is a chart showing results of φ (PHI) scan of the (1 1 2 -2)plane of a sample Ti layer shown in FIG. 14;

FIG. 16 is a chart showing results of φ (PHI) scan of the (1 0 1 -2)plane of the Ti layer evaporated on the (100) plane of the Si baselayer;

FIG. 17 is a chart showing results of φ (PHI) scan of the (1 2 2 -2)plane of the sample Ti layer shown in FIG. 16;

FIG. 18 is a cross sectional view showing the structure of asemiconductor device according to a first embodiment of the presentinvention;

FIG. 19 is a cross sectional view showing the structure of asemiconductor device according to a second embodiment of the presentinvention;

FIG. 20 is a cross sectional view showing the structure of asemiconductor device according to a third embodiment of the presentinvention;

FIG. 21 is a cross sectional view showing the structure of asemiconductor device according to a fourth embodiment of the presentinvention; and

FIG. 22 is a cross sectional view showing a modification of the fourthembodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment of the present invention has a structure that sapphire isemployed to form a base layer of a substrate. Moreover, single crystalTi layer is evaporated on the surface of the sapphire base layer.

FIG. 1 shows dependency of the crystallinity of single crystal Ti on thethickness.

Conditions under which the results shown in FIG. 1 are obtained are asfollows:

Evaporating Speed: 0.5 nm/s

Evaporation Temperature: 150° C.

Thickness: subjects which must be measured

The y axis of the graph shown in FIG. 1 stands for an average intensity(a relative value) of six peaks obtained by φ (PHI) scanning the Tilayer. The crystallinity is proportional to the intensity shown on the yaxis. The thickness of Ti layer of measured sample is same. As a matterof course the Ti layer which is a base layer of the AlGaInNsemiconductor layer must have high crystallinity to improve thecrystallinity of the AlaInN type semiconductor layer. The φ (PHI) showssix peaks corresponding to (1 0 1 -2) planes of a hexagonal system whenthe sample is rotated by 360°.

As described above, the Ti layer on which six peaks have been observedby the φ (PHI) scan is considered to be in the for, of single crystal orclose to the single crystal.

As for the φ (PHI) scan, refer to Journal of Electronic Materials, Vol.25, No. 11, pp. 1740-1747, 1996.

To obtain the results shown in FIG. 1, the following previous process isperformed before the Ti layer is formed.

Conditions under which the Ti layer was formed with the results shown inFIG. 6 were as follows:

The sapphire substrate is set in a chamber for evaporation, and then avacuum pump which is usually employed in industrial fields is operatedto produce a vacuum of 3×10⁻⁵ Torr. Then, the chamber is filled withnitrogen gas. The above-mentioned process is repeated three times sothat oxygen in the chamber is reduced and oxidation of Ti is prevented.Therefore, another method which is capable of sufficiently dischargingoxygen from the chamber may be employed.

As a result of an investigation performed by the inventors, theabove-mentioned nitrogen purge must be repeated because the degree ofvacuum of a vacuum apparatus provided for an evaporating apparatus,which is usually employed in industrial fields, is limited (usuallylimited to 10⁻⁷ Torr). As a matter of course, another inert gas may beemployed in place of the nitrogen gas.

Then, the pressure of the nitrogen gas is lowered to 8×10⁻⁷ Torr.

After the foregoing previous process has been completed, the substrateis heated to a predetermined temperature with a lamp heater. Moreover,bulks of Ti are irradiated with electron beams so as to be melted sothat single crystal Ti layer is formed on the sapphire base layer.

The φ (PHI) scan was performed by using a four-axis single crystaldiffractometer (trade name: “X-pert” manufactured by Philips)(hereinafter identical).

FIG. 2 shows an example of results of φ (PHI) scanning (when thethickness of the Ti layer: 300 nm). The averages (relative values) ofintensities of six peaks corresponding to (101-2) planes of Ti allowedto appear in FIG. 2 are values of the axis of ordinate shown in FIG. 1.

In accordance with the results shown in FIG. 1, it is preferable thatthe thickness of the Ti layer which is formed on the surface of amaterial except for Ti is 1000 to 15000 angstrom (100 nm to 1500 nm). Ifthe thickness of the Ti layer is smaller than 100 nm, satisfactorycrystallinity cannot be obtained. The Ti layer is not required to have athickness larger than 1500 nm. In this case, long time is required toform the film. If sufficiently long time is permitted, the necessity ofdetermining an upper limit can be eliminated.

Since the Ti layer having the above-mentioned thickness is formed, aportion of light emitted by the GaN type semiconductor layer anddischarged toward the substrate is reflected by the Ti layer. Thus,light penetration is inhibited. Therefore, light generated by the GaNtype semiconductor layer is substantially fully extracted from thesurface of the device. Thus, light can effectively be used.

More preferably, the thickness of the Ti layer is 2000 angstrom to 10000angstrom (200 nm to 1000 nm).

FIG. 3 shows dependency of the crystallinity of the evaporated Ti filmon the sapphire substrate.

The axis of ordinate of the graph stands for average intensities(relative values) obtained by the φ (PHI) scan.

Conditions under which the results shown in FIG. 3 are obtained are asfollows:

Evaporating Speed: subjects which must be measured

Evaporation Temperature: 150° C.

Thickness: 300 nm

As can be understood from the results shown in FIG. 3, it is preferablethat the evaporating speed of the Ti layer is 0.5 nm/s or higher. Notethat the evaporating speed of Ti which is 2 nm/s or higher isimpractical because surface morphology deteriorates.

FIG. 4 shows dependency of the crystallinity of the evaporated Ti filmon the evaporation temperature (the temperature of the substrate duringthe evaporation process) on the sapphire base layer. The axis ofordinate of the graph stands for average intensities (relative values)obtained by the φ (PHI) scan.

Conditions under which the Ti layer was formed when the results shown inFIG. 4 were as follows:

Evaporating Speed: 0.5 nm/s

Evaporation Temperature: subjects which must be measured

Thickness: 300 nm

As can be understood from the results shown in FIG. 4, an expectationcan be held that satisfactory crystallinity can be realized at roomtemperature to 350° C., more preferably 25° C. to 250° C., mostpreferably 150° C. to 250° C.

In accordance with an investigation made by the inventory of the presentinvention, it is preferable that the evaporation temperature is 130° C.to 170° C., more preferably 150° C. If the temperature is higher than170° C., there is apprehension that orientation characteristic of Ti inthe axis c deteriorates.

FIG. 5 shows dependency of the crystallinity of the evaporated Ti filmon the heat treatment temperature on the sapphire substrate.

Conditions under which the Ti layer was formed when the results shown inFIG. 5 were as follows:

Evaporating Speed: 0.5 nm/s

Evaporation Temperature: 150° C.

Thickness: 300 nm

The thus-obtained Ti/sapphire was heated in a heating furnace to eachtemperature shown on the axis of abscissa (for five minutes).

Similarly to FIG. 1, the axis of ordinate of the graph stands foraverage intensities (relative values) obtained by the φ (PHI) scan.

An can be understood from the results shown in FIG. 5, the crystallinitydeteriorates if the Ti layer on sapphire substrate is heated to a levelhigher than 750° C. Namely, it is preferable that the Ti layer ismaintained at a temperature not higher then 750° C. until at least oneAlGaInN semiconductor layer is formed on the Ti layer. After the firstAlGaInN semiconductor layer has been formed, a second GaN typesemiconductor layer can be formed on the first GaN type semiconductorlayer. Therefore, the temperature at which the crystallinity of thefirst AlGaInN semiconductor layer can be maintained is a criticaltemperature. Even if the crystallinity of the Ti layer deteriorates atthe foregoing critical temperature and the crystallinity of the firstAlGaInN type semiconductor layer is maintained, the crystallinity of thesecond AlGaInN type semiconductor layer is not affected adversely.

As can be understood from the results shown in FIG. 5, it is preferablethat the Ti layer is maintained at a temperature not higher than 600° C.until at least one AlGaInN type semiconductor layer is grown on the Tilayer.

FIG. 6 shows results of 2θ-ω (2θ:20° to 100°) scan performed for thepurpose of evaluating the crystallinity of a GaN layer grown on an AlNbuffer layer formed on the Ti layer formed on the sapphire base layer.Also the 2θ-ω scan was performed with the four-axis single crystaldiffractometer (trade name: X-pert manufactured by Philips) (hereinafteridentical to following 2θ-ω scan).

Conditions under which the Ti layer was formed with the results shown inFIG. 6 were as follows:

Evaporating Speed: 0.5 nm/s

Evaporation Temperature; 150° C.

Thickness: 300 nm

The following measurement was performed such that the Ti layer wasformed under the same condition.

Before the AlN buffer layer was formed, the Ti/sapphire was heated at600° C. for 5 minutes in a vacuum (3×10⁻⁵ Torr) (vacuum cleaning).

The AlN buffer layer was formed by the MOCVD method under the followingconditions:

Pressure in Reaction Chamber; Atomospheric pressure

Temperature: 400° C.

Material Gas 1: Ammonia

Material Gas 2: TMA

Carrier Gas: H₂

The GaN layer was formed by the MOCVD method under the followingconditions;

Pressure in Reaction Chamber: Atomospheric pressure

Temperature: 1000° C.

Material Gas 1: Ammonia

Material Gas 2: TMG

Carrier Gas: H₂

Conditions under which the GaN layer is formed in the following casesare the same as those of the foregoing,

FIG. 7 shows results of φ (PHI) scanning of the same material as thatshown in FIG. 6.

As can be understood from the results shown in FIGS. 6 and 7, GaN grownon the Ti/sapphire through the AlN buffer layer, preferredcrystallinity. Therefore, when the AlGaInN type semiconductor layer isgrown on the AlN/Ti/sapphire base layer, a semiconductor device, such asa light emitting device, which has a sapphire function can be formed bydint of the above-mentioned semiconductor layer.

FIG. 8 shows results of 2θ-ω (2θ: 20° to 100°) scan performed for thepurpose of evaluating the crystallinity of a GaN Layer grown on an AlGaNbuffer layer formed on the Ti layer formed on the sapphire base layer.

Before the AlGaN buffer layer was formed, the Ti/sapphire base layer washeated at 600° C. for 5 minutes in a vacuum (3×10⁻⁵ Torr) (vacuumcleaning).

The AlGaN buffer layer was formed by the MOCVD method under thefollowing conditions:

Pressure in Reaction Chamber: Atomospheric pressure

Temperature: 300° C.

Material Gas 1: Ammonia

Material Gas 2: TMA

Material Gas 3: TMG

Carrier Gas: H₂

The GaN layer was formed by the MOCVD method under the same conditionsas those shown in FIGS. 6 and 7.

FIG. 9 shows results of φ (PHI) scan or the same material as those shownin FIG. 8.

As can be understood from the results shown in FIGS. 8 and 9, GaN grownon the Ti/sapphire through the AlGaN buffer layer has satisfactorycrystallinity.

As can be understood from the results shown in FIGS. 6 and 7, the GaNlayer formed on an AlGaN buffer layer has satisfactory crystallinitycompared with GaN layer formed on an AlN buffer layer.

FIG. 10 shows a rocking curve for evaluating the crystallinity of GaNgrown on the Ti/sapphire through the AIGaN buffer layer. As a result ofthe rocking curve above, one ordinarily skilled in the art is able tofind that the foregoing GaN has satisfactory characteristics to serve asthe semiconductor layer for constituting the light emitting device.

FIG. 11 shows the relationship between the growth temperature of theAlGaN buffer layer and the crystallinity of GaN.

The axis of ordinate of the graph stands for average intensities(relative values) of six peaks obtained by the φ (PHI) scan similarly tothat shown in FIG. 9.

The Ti layer was formed under the above-mentioned conditions.

The Ti layer was cleaned by making the inside portion of the chamber(3×10⁻⁵ Torr) at 600° C. for 5 minutes.

The AlGaN buffer layer was formed by the MOCVD method under thefollowing conditions:

Pressure in Reaction Chamber: Normal pressure

Temperature: subject which must be measured

Material Gas 1: Ammonia

Material Gas 2: TMA

Material Gas 3: TMG

Carrier Gas: H₂

Flow Rate (TMG/(TMG+TMA) of Carrier Gases: 0.625

As can be understood from the results shown in FIG. 11, it is preferablethat the temperature at which the AlGaN buffer layer is grown is 250° C.to 350° C., more preferably 280° C. to 330° C., most preferably about300° C.

FIG. 12 shows the relationship between the flow rate ratio of TMG andTMA carrier gases when the AlGaN buffer layer is formed and thecrystallinity of GaN. The axis of ordinate of the graph stands foraverage intensities (relative values) of six peaks obtained by the φ(PHI) scan similarly to that shown in FIG. 9.

The Ti layer was formed under the above-mentioned conditions.

The Ti layer was cleaned by making the inside portion of the chamber(3×10⁻⁵ Torr) at 600° C. for 5 minutes.

The AlGaN buffer layer was formed by the MOCVD method under thefollowing conditions:

Pressure in Reaction Chamber: Normal pressure

Temperature: 300° C.

Material Gas 1: Ammonia

Material Gas 2: TMA

Material Gas 3: TMG

Carrier Gas: H₂

Flow Rate (TMG/(TMG+TMA) of Carrier Gases: subject to be measured

The GaN layer was formed under the above-mentioned conditions.

As can be understood from the results shown in FIG. 12, it is preferablethat the flow rate of the carrier gases is such that TMG/(TMG+TMA)=0.4to 0.8. Therefore, it is preferable that the molar ratio of the materialgases which are supplied into the reaction chamber is such thatTMG/(TMG+TMA)=0.53 to 0.87, more preferably the flow rate 0.5 to 0.7(the molar ratio=0.63 to 0.80), most preferably the flow rate=0.60 to0.65. It is considered at present that the most preferred flowrate=0.625 (the molar ratio=0.737).

In accordance with results of an investigation performed by theinventors of the present invention, when the flow rate of the carriergases was made such that TMG/(TMG+TMA) 0.625 under the conditions whenthe results shown in FIG. 12 were obtained, the composition of thebuffer layer was Al_(0.9)Ga_(0.1)N,

It is preferable that the Al_(a)Ga_(1-a)N buffer layer has a structurethat the composition ratio a of Al is 0.85 to 0.95, more preferablysubstantially 0.9.

FIG. 13 shows the relationship between the cleaning temperature of theTi/sapphire and the crystallinity of GaN. The axis of ordinate of thegraph stands for average intensities (relative values) of six peaksobtained by the φ (PHI) scan similarly to that shown in FIG. 9.

The Ti layer was formed under the above-mentioned conditions. The AlGaNbuffer layer and the GaN layer were formed under the same conditions asthose shown in FIG. 8.

Results of cleaning indicated by closed triangles were obtained when asapphire base layer on which Ti was evaporated was placed in the MOCVDchamber, the pressure of which was made to be vacuum (the degree ofvacuum: 3×10⁻⁵ Torr). Then, the lamp heater was turned on to heat thesubstrate to a predetermined temperature, and then the foregoingtemperature was maintained for 5 minutes. Then, the substrate wascooled.

On the other hand, results of cleaning indicated by open triangles (Δ)were obtained when the sapphire base layer on which Ti layer wasevaporated was placed in the MOCVD chamber to which hydrogen wassupplied (atmospheric pressure in the chamber). Then, the lamp heaterwas turned on to heat the substrate to a predetermined level, and thenthe temperature was maintained for 5 minutes. Then, the substrate wascooled.

As can be understood from the results shown in FIG. 13, a GaN layerhaving satisfactory crystallinity can be obtained when Ti is heated in avacuum so as to be treated thermally between evaporation of the Ti layeron the sapphire base layer and forming of the buffer layer.

It is preferably that the cleaning temperature is 500° C. to 750° C.,more preferably 550° C. to 700° C. and most preferably 600° C. to 650°C.

The degree of vacuum required in the cleaning operation is not limitedparticularly. To sufficiently remove impurities from the Ti layer, it ispreferable that the degree of vacuum must be raised as much as possible.

The combination of the sapphire base layer and the Ti layer has beendescribed. It can be considered that similar results can be obtainedfrom a structure in which a Ti layer is formed on a substrate made of Sior another material.

FIG. 14 shows dependency of the crystallinity of Ti evaporated on the(111) plane of the Si substrate on cleaning of wafer Ti was evaporatedunder the following conditions (which are the same as those for thesapphire base layer):

Evaporating Speed: 0.5 nm/s

Evaporation Temperature: 150° C.

Thickness: 300 nm

Results of a process were indicated by a solid line shown in FIG. 14,the process being performed such that the Si base layer was subjected tonitrogen purge similarly to the process for the sapphire base layer sothat oxygen was substantially removed from the inside portion of thechamber. Thus, a Ti layer was formed on the (111) plane. FIG. 14 showsresults of φ (PHI) scan of the (1 0 1 -2) plane of the Ti layer. Adashed line shown in FIG. 14 shows results of cleaning of the Si baselayer with buffered hydrofluoric acid before the nitrogen purge isperformed.

FIG. 15 shows results of φ (PHI) scan of the (1 1 2 -2) plane of thesample Ti layer.

As can be understood from the result shown in FIGS. 14 and 15, the Tilayer evaporated on the S1 base layer previously cleaned with thebuffered hydrofluoric acid has satisfactory crystallinity. On the otherhand, the crystallinity of the Ti layer evaporated on the Si base layerby emitting the acid cleaning is unsatisfactory.

FIG. 16 shows results of φ (PHI) scan of the (101-2) plane of the Tilayer evaporated on the (100) plane of the Si base layer, similar tothose shown in FIG. 14.

FIG. 17 similarly shows results of φ (PHI) scan of the (112-2) plane ofthe Ti layer evaporated on the (100) plane of the Si substrate.

As can be understood from the results shown in FIGS. 16 and 17, the Tilayer evaporated on the (100) plane of the Si base layer hasunsatisfactory crystallinity regardless of acid cleaning.

As can be understood from the results shown in FIGS. 14 to 17, thesingle crystal Ti layer can be formed on the Si base layer byevaporating Ti on the (111) plane of the Si base layer and by previouslycleaning the Si base layer with buffered hydrofluoric acid orhydrofluoric acid.

A first embodiment of the present invention will now be described.

In this embodiments a light emitting diode 10 is described which has astructure as shown in FIG. 19.

Specifications of semiconductor layers are as follows:

Layer Composition Dopant (Thickness) p Clad Layer 6 p-GaN Mg (0.3 μm)Light Emitting Layer 5 (Superlattice Structure) Quantum Well LayerIn_(0.15)Ga_(0.85)N (3.5 nm) Barrier Layer GaN (3.5 nm) (Number ofRepetition of Quantum Well Layer and Barrier Layer: 1 to 10) n CladLayer 4 n-GaN Si   (4 μm) Buffer Layer 3 Al_(0.9)Ga_(0.1)N  (15 nm) TiLayer 2 Ti Single Crystal (300 nm)  Substrate 1 Sapphire (300 μm) 

The n clad layer 4 may be formed into a double-layered structureconsisting of a low electron density n layer adjacent to the lightemitting layer 5 and a high electron density n⁺ layer adjacent to thebuffer layer 3.

The structure of the light emitting layer 5 is not limited to thesuperlattice structure and it may be a single hetero structure, a doublehetero structure or a homogeneous structure or the like.

An Al_(x)In_(y)Ga_(1-x-y)N (including X=0, Y=0 or X=Y=0) layer to whichan acceptor, such as magnesium has been doped, and which has a wide bandgap may be interposed between the light emitting layer 5 and the p cladlayer 6. Thus, dispersion of electrons implanted into the light emittinglayer b in the p clad layer 6 can be prevented.

The p clad layer S may be formed into a double-layered structureconsisting of a low hall density p layer adjacent to the light emittinglayer 5 end a high hall density p⁺ layer adjacent to the lighttransmissive electrode 7.

The process which it performed until the buffer layer 3 is formed issimilar to that performed when the results shown in FIG. 10 wereobtained.

Each of the GaN type semiconductor layers is formed by the known MOCVDmethod. The foregoing growing method is performed such that ammonia gasand alkyl compound gas of an element in a group III, for example,trimethyl gallium (TMG), trimethyl aluminum (TMA) or trimethylindium(TMI) are supplied to a substrate heated to an appropriate temperatureso that a heat decomposition reaction of the supplied materials isperformed. Thus, required crystal is grown on the substrate.

The transparent electrode 7 is in the form of a thin film containinggold. The electrode 7 is formed to cover substantially the overall uppersurface of the p clad layer 6. Also the p electrode is made of amaterial containing gold, the p electrode 8 being formed on theelectrode 7 by evaporation.

The n electrode 9 is evaporated on the n clad layer 4.

FIG. 19 shows a semiconductor device according to a second embodiment ofthe present invention. The semiconductor device according to thisembodiment is a light emitting diode 20. The same elements as those ofthe light emitting diode 10 shown in FIG. 18 and according to the firstembodiment are given the same reference numerals and the same elementsare omitted from description.

That is, the light emitting diode 20 according to this embodiment has astructure that the buffer layer 23 is made of AlN.

FIG. 20 shows a semiconductor device according to a third embodiment ofthe present invention. The semiconductor device according to thisembodiment is a light emitting diode 30. The same elements as those ofthe light emitting diode 10 shown in FIG. 18 and according to the firstembodiment are given the same reference numerals and the same elementsare omitted from description.

That is, the light emitting diode 30 according to this embodiment has astructure that the buffer layer is omitted. In this case the n cladlayer is formed by the MBE method.

FIG. 21 shows a semiconductor device according to a fourth embodiment ofthe present invention. The semiconductor device according to thisembodiment is a light emitting diode 40.

Specifications of semiconductor layers are as follows:

Layer Composition Dopant (Thickness) P Clad Layer 46 p-GaN Mg (0.3 μm)Light Emitting Layer 45 (Superlattice Structure) Quantum Well LayerIn_(0.15)Ga_(0.85)N (3.5 nm) Barrier Layer GaN (3.5 nm) (Number ofRepetition of Quantum Well Layer and Barrier Layer: 1 to 10) N CladLayer 44 n-GaN Si   (4 μm) Buffer Layer 43 Al_(0.9)Ga_(0.1)N  (15 nm) TiLayer 42 Ti Single Crystal (300 nm)  Substrate 41 Si (111) plane (300μm) 

The AlGaN buffer layer 43 may be replaced by a layer made of AlNsimilarly to the second embodiment. Similarly to the third embodiment,the buffer layer 43 may be omitted.

As described in the first embodiment, the GaN semiconductor layers 44 to46 may be replaced by layers having other structures. Also the methodsfor forming the layers aye similar to those according the firstembodiment. If the buffer layer is omitted the GaN semiconductor layeradjacent to the Ti layer is formed by the MBE method.

In the foregoing process, the method of forming the Ti layer 42 issimilar to that when the results indicated by the dashed line shown inFIG. 14 were obtained.

The AlGaN buffer layer 43 was formed similarly to the first embodiment.

The transparent electrode 47 is in the form of a thin film containinggold, the transparent electrode 47 being formed on substantially theoverall upper surface of the p clad layer 46. Also the p electrode 48 ismade of a material containing gold, the p electrode 48 being formed onthe transparent electrode 47 by evaporation.

The substrate 41 can as it is be used as the n electrode.

FIG. 22 shows a modification of the fourth embodiment. The same layersas those shown in FIG. 21 are given the same reference numerals and thesame layers are omitted from description.

As shown in FIG. 22, the p clad layer 46, the light emitting layer 45and the n clad layer 44 may sequentially be grown on the buffer layer 43so as to constitute a light emitting device 50. Since the device 50 hasthe structure that the n clad layer 44 having low resistance forms theuppermost surface, the foregoing transparent electrode (referencenumeral 47 shown in FIG. 21) have a possibility to be able to beomitted.

Reference numeral 58 in the drawing represents an n electrode. The baselayer 41 can as it is be used as the p electrode.

The semiconductor device having the above-mentioned structure andaccording to the fourth embodiment has the structure that the Ti layerserves as a buffer layer for buffering stress. Therefore, a crack causedfrom the difference in the coefficient of thermal expansion between theSi base layer and the AlGaInN type semiconductor cannot substantiallyreach the GaN semiconductor layer.

The device to which the present invention is applied is not limited tothe above-mentioned emitting diode. The present invention may be appliedto a light device, such as a light receiving diode and a laser diode oran electronic device such as the FET structure.

Also the present invention may be applied to a laminated material whichis an intermediate member of the foregoing device.

It is understood that the present disclosure of the preferred form canbe changed in the details of construction and in the combination andarrangement of parts which can be carried out by an expert withoutdeparting from the spirit and the scope of the invention as claimed.

The following structures are disclosed:

(1) A method of forming substantially single crystal Ti layer on asapphire base layer, comprising the steps of preparing a sapphire baselayer; and evaporating or sputtering Ti on the sapphire base layer in anenvironment from which oxygen has substantially been removed.

(2) A method according to structure (1), wherein speed at which the Tilayer is formed is 0.5 nm/s or higher.

(3) A method according to structure (1), wherein a temperature at whichthe Ti layer is formed is substantially 250° C.

(4) A method according to structure (1), wherein a temperature at whichthe Ti layer is formed is room temperature to 150° C.

(5) A method according to any one of structures (1) to (4) wherein thethickness of the Ti layer is 100 nm to 1500 nm.

(6) A method according to any one of structures (1) to (4), wherein thethickness of the Ti layer is 200 nm to 1000 nm.

(7) A method according to any one of structures (1) to (6), wherein thesurrounding environment from which oxygen has been removed is realizedby making the inside portion of a chamber of an evaporating apparatus tobe a vacuum, by performing a process for filling the chamber with inertgas one or a plurality of times and by making the inside portion of thechamber to be a vacuum.

(8) A method of forming a substantially single crystal Ti layer an a Sisubstrate, comprising the steps of:

preparing a Si base layer;

cleaning the Si base layer with acid; and

forming Ti on the (111) plane of the Si base layer in a surroundingenvironment from which oxygen has substantially been removed.

(9) A method according to structure (8), wherein the cleaning isperformed with solution containing hydrofluoric acid or bufferedhydrofluoric acid.

(10) A method according to structure (8) or (9), wherein speed at whichthe Ti layer is formed is 0.5 nm/s or higher.

(11) A method according to structure (8) or (9), wherein a temperatureat which the Ti layer is formed is room temperature to 250° C.

(12) A method according to structure (8) or (9), wherein a temperatureat which the Ti layer is formed is about 150° C.

(13) A method according to any one of structures (8) to (12), whereinthe thickness of the Ti layer is 100 nm to 1500 nm.

(14) A method according to any one of structures (8) to (12), whereinthe thickness of the Ti layer is 200 nm to 1000 nm.

(15) A method according to any one or structures (8) to (14), whereinthe surrounding environment from which oxygen has been removed itrealized by making the inside portion of a chamber of an evaporatingapparatus to be a vacuum, by performing a process for filling thechamber with inert gas one or a plurality of times and by making theinside portion of the chamber to be a vacuum.

(16) A method of growing a GaN type semiconductor layer, comprising thestep for heating Ti single crystal surface at a reduced pressure beforea GaN type semiconductor layer is formed on the Ti single crystalsurface.

(17) A method according to structure (16), wherein a heating temperatureis 500° C. to 750° C.

(18) A method according to structure (17), wherein a heating temperatureis 550° C. to 700° C.

(19) A method according to structure (16), wherein a heating temperatureis 600° C. to 650° C.

What is claimed is:
 1. A method of manufacturing a GaN semiconductordevice, said method comprising: preparing a substrate; forming a Tilayer on said substrate; and forming a GaN semiconductor layer on saidTi layer, wherein said Ti layer is formed on said substrate so that anoverall body of said GaN semiconductor device comprises substantiallysingle crystal Ti.
 2. A method of manufacturing a semiconductor deviceaccording to claim 1, further comprising substantially removing oxygenfrom the atmosphere of said substrate before said Ti layer is formed. 3.A method of manufacturing a semiconductor device according to claim 1,wherein a film forming rate of said Ti layer is 0.5 nm/s or higher.
 4. Amethod of manufacturing a semiconductor device according to claim 1,wherein a temperature at which said Ti layer is formed is a level fromroom temperature to 250° C.
 5. A method of manufacturing a semiconductordevice according to claim 1, wherein a temperature at which said Tilayer is formed is 150° C.
 6. A method of manufacturing a semiconductordevice according to claim 1, wherein said substrate is made of sapphire,and said Ti layer is evaporated on said sapphire substrate.
 7. A methodof manufacturing a semiconductor device according to claim 1, whereinsaid substrate is made of Si, and said Ti layer is evaporated on said Sisubstrate.
 8. A method of manufacturing a semiconductor device accordingto claim 7, wherein said Ti layer is formed on a (111) plane of said Sisubstrate.
 9. A method of manufacturing a semiconductor device accordingto claim 7, wherein said Si substrate is cleaned with acid before saidTi layer is formed.
 10. A method of manufacturing a semiconductor deviceaccording to claim 9, wherein said cleaning operation using acid isperformed with solution which contains hydrofluoric acid or bufferedhydrofluoric acid.
 11. A method of manufacturing a semiconductor deviceaccording to claim 1, further comprising forming a buffer layer made ofAlaInbGal-a-bN (a=0, b=0 including a=b=0) between said Ti layer and saidGaN semiconductor layer.
 12. A method of manufacturing a semiconductordevice according to claim 11, further comprising cleaning said Ti layerin a vacuum before said buffer layer is formed.
 13. A method ofmanufacturing a semiconductor device according to claim 12, wherein saidvacuum cleaning is performed such that said Ti layer is heated to 500°C. to 750° C. in substantially a vacuum.
 14. A method of manufacturing asemiconductor device according to claim 12, wherein said vacuum cleaningis performed such that said Ti layer is heated to 550° C. to 750° C. insubstantially a vacuum.
 15. A method of manufacturing a semiconductordevice according to claim 12, wherein said vacuum cleaning is performedsuch that said Ti layer is heated to 600° C. to 650° C. in substantiallya vacuum.
 16. A method of manufacturing a semiconductor device accordingto claim 1, further comprising growing a buffer layer made of AlGaNbetween said Ti layer and said GaN semiconductor layer at a temperaturefrom 250° C. to 350° C.
 17. A method of manufacturing a semiconductordevice according to claim 1, further comprising growing a buffer layerof AlGaN between said Ti layer and said GaN semiconductor layer at atemperature from 280° C. to 330° C.
 18. A method of manufacturing asemiconductor device according to claim 1, further comprising growing abuffer layer made of AlGaN between said Ti layer and said GaNsemiconductor layer at a temperature of about 300° C.
 19. A method ofmanufacturing a semiconductor device according to claim 1, furthercomprising growing a buffer layer made of AIGaN between said Ti layerand said GaN semiconductor layer at a molar ratio which is Ga materialgas/(Ga material gas+Al material gas)=0.53 to 0.87.
 20. A method ofmanufacturing a semiconductor device according to claim 1, furthercomprising growing a buffer layer made of AlGaN between said Ti layerand said GaN semiconductor layer at a molar ratio which is Ga materialgas/(Ga material gas+A1 material gas)=0.63 to 0.80.
 21. A method ofmanufacturing a semiconductor device according to claim 1, furthercomprising growing a buffer layer made of AlGaN between said Ti layerand said GaN semiconductor layer at a molar ratio which is Ga materialgas/(Ga material gas+A1 material gas)=about 0.737.
 22. A method ofmanufacturing a semiconductor device according to claim 1, wherein saidTi layer is maintained at 750° C. or lower until at least one GaNsemiconductor layer is formed.
 23. A method of manufacturing asemiconductor device according to claim 1, wherein said Ti layer ismaintained at 600° C. or lower until at least one GaN semiconductorlayer is formed.
 24. A method of manufacturing a semiconductor deviceaccording to claim 1, wherein said semiconductor device is one of alight emitting device and a light receiving device.
 25. The method ofclaim 1, wherein said Ti layer is formed by one of evaporation andsputtering.
 26. A method of manufacturing a laminated member, saidmethod comprising: preparing a substrate; forming a Ti layer on saidsubstrate; and forming a GaN semiconductor layer on said Ti layer;wherein said Ti layer is formed on said substrate so as to cause anoverall body of said laminated member to comprise substantially singlecrystal Ti.
 27. A method of manufacturing a laminated member accordingto claim 26, further comprising substantially removing oxygen from theatmosphere of said substrate before said Ti layer is formed.
 28. Amethod of manufacturing a laminated member according to claim 26,wherein a film forming rate of said Ti layer is 0.5 nm/s or higher. 29.A method of manufacturing a laminated member according to claim 26,wherein, a temperature at which said Ti layer is formed is a level fromroom temperature to 250° C.
 30. A method of manufacturing a laminatedmember according to claim 26, wherein a temperature at which said Tilayer is formed is 150° C.
 31. A method of manufacturing a laminatedmember according to claim 26, wherein said substrate is made ofsapphire, and said Ti layer is evaporated on said sapphire substrate.32. A method of manufacturing a laminated member according to claim 26,wherein said substrate is made of Si, and said Ti layer is evaporated onsaid Si substrate.
 33. A method of manufacturing a laminated memberaccording to claim 32, wherein said Ti layer is formed on a (111) planeof said Si substrate.
 34. A method of manufacturing a laminated memberaccording to claim 32, wherein said Si substrate is cleaned with acidbefore said Ti layer is formed.
 35. A method of manufacturing alaminated member according to claim 34, wherein said cleaning operationusing acid is performed with solution which contains hydrofluoric acidor buffered hydrofluoric acid.
 36. A method of manufacturing a laminatedmember according to claim 26, further comprising forming a buffer layermade of AlaInbGal-a-bN (a=0, b=0 including a=b=0) between said Ti layerand said GaN semiconductor layer.
 37. A method for manufacturing alaminated member according to claim 36, further comprising cleaning saidTi layer in a vacuum before said buffer layer is formed.
 38. A methodfor manufacturing a laminated member according to claim 37, wherein saidvacuum cleaning is performed such that said Ti layer is heated to 500°C. to 750° C. in substantially a vacuum.
 39. A method for manufacturinga laminated member according to claim 37, wherein said vacuum cleaningis performed such that said Ti layer is heated to 550° C. to 700° C. insubstantially a vacuum.
 40. A method for manufacturing a laminatedmember according to claim 37, wherein said vacuum cleaning is performedsuch that said Ti layer is heated to 600° C. to 650° C. in substantiallya vacuum.
 41. A method of manufacturing a laminated member according toclaim 26, further comprising growing a buffer layer made of AlGaNbetween said Ti layer and said GaN semiconductor layer at a temperaturefrom 250° C. to 350° C.
 42. A method for manufacturing a laminatedmember according to claim 26, further comprising growing a buffer layermade of AlGaN between said Ti layer and said GaN semiconductor layer ata temperature from 280° C. to 330° C.
 43. A method for manufacturing alaminated member according to claim 26, further comprising growing abuffer layer made of AlGaN between said Ti layer and said GaNsemiconductor layer at a temperature of about 300° C.
 44. A method formanufacturing a laminated member according to claim 26, furthercomprising growing a buffer layer made of AlGaN between said Ti layerand said GaN semiconductor layer at a molar ratio which is Ga materialgas/(Ga material gas+A1 material gas)=0.53 to 0.87.
 45. A method formanufacturing a laminated member according to claim 26, furthercomprising growing a buffer layer made of AlGaN between said Ti layerand said GaN semiconductor layer at a molar ratio which is Ga materialgas/(Ga material gas+A1 material gas)=0.63 to 0.80.
 46. A method formanufacturing a laminated member according to claim 26, furthercomprising growing a buffer layer made of AlGaN between said Ti layerand said GaN semiconductor layer at a molar ratio which is Ga materialgas/(Ga material gas+A1 material gas)=about 0.737.
 47. A method ofmanufacturing a laminated member according to claim 26, wherein said Tilayer is maintained at 750° C. or lower until at least one GaNsemiconductor layer is formed.
 48. A method of manufacturing a laminatedmember according to claim 26, wherein said Ti layer is maintained at600° C. or lower until at least one GaN semiconductor layer is formed.49. The method of claim 26, wherein said Ti layer is formed by one ofevaporation and sputtering.